The present invention relates to a rotary compressor and, more particularly, to the control of refrigeration power of an air conditioning system employing a rotary compressor.
Ordinary rotary compressors of the sliding vane type are finding spreading use as compressors of automobile air conditioners, because of a compact and simple construction as compared with conventional reciprocating type compressors which have a large number of parts and complicated construction. In comparison with the reciprocating type compressors, however, the known sliding vane type rotary compressors suffer the following disadvantages.
Namely, when such a rotary compressor is used as a compressor of an automobile air conditioner, the rotary shaft of the compressor is driven by the power of the engine through a clutch having a pulley which is driven by the engine power via a belt. Therefore, the refrigerating capacity of the air conditioner employing the sliding vane type compressor is increased substantially linearly in proportion to the speed of the engine.
On the other hand, when the reciprocating type compressor is used as a compressor for an automobile air conditioner, the suction valve of the compressor cannot satisfactorily follow up the operation of the compressor particularly at high operation speeds which impedes the sucking of refrigerant gas into the cylinders. In consequence, the refrigerating capacity is saturated when the operation speed of the compressor is increased beyond a predetermined speed. In other words, the excessive increase of the refrigerating capacity is automatically suppressed during high speed running of the automobile in an air conditioner employing a reciprocating type compressor. Such an automatic suppressing function cannot be performed by the rotary compressor. Therefore, in an automobile air conditioner employing the rotary type compressor, the efficiency is inconveniently lowered due to an increase of the compression work, or the air is cooled excessively, during high speed running of the automobile.
In order to avoid the above-described problem of the rotary compressor, it has been proposed to provide a control valve in a passage leading to a suction port formed in one of the side walls of the compressor, the control valve being adjusted to vary the opening area of the passage in relation to the engine speed such that the opening area is reduced as the engine speed is increased, thereby to control the refrigerating capacity. This arrangement, however, requires an additional installation of the control valve, which in turn complicates the construction and raises the production cost.
As another measure for eliminating the drawback of the rotary compressor, i.e. excessive refrigerating capacity at high speed operation, it has been proposed also to adopt such a construction as adapted to prevent the operation speed from being increased above a predetermined speed, by employing a fluid clutch, planetary gear system and so forth. The construction employing the fluid clutch, however, is accompanied by a loss of energy due to generation of heat at the relatively moving surfaces. On the other hand, the construction incorporating the planetary gear system makes the size of the compressor large due to the addition of the planetary gear system having a large number of parts. This goes quite contrary to the current demand for simplification of compressor and reduction of the size of the same to cope with the requirement saving of energy.